_BLACK_ exhaust

bought this 98 altima a couple weeks ago, and i've noticed the rear of my car keeps getting really blackened from what looks like exhaust smoke. there's no holes or anything in the tailpipe, everything looks brand new. it's getting all over my trunk on that side of the car too. the rain yesterday washed it away, but i just got home from work and noticed it's there again.

is this a sure sign that i'm burning oil, or is there another way to check? the car's only got 127000km on it. i've been told my gas could be running rich from shifting too early, but i'm pretty sure i'm driving the car just fine. the car does seem to be running kind of loudly, but i can't say for sure if it's related.

can anybody give me some input as to what it could be? thanks.

Black is fuel. Blue is oil. White is coolant.

Take a look at your spark plugs if you have the means to. See what they tell you.